1. Field of the Invention
The present invention relates to ultrasonic motors and, more particularly, to an ultrasonic motor in which a moving body pressure-bonded to a specific surface is relatively moved in a desired direction with respect to an ultrasonic oscillator or piezoelectric transducer, by ultrasonic oscillation which is generated on the specific surface of the ultrasonic oscillator.
2. Related Art and Prior Art Statement
Conventionally, various kinds of ultrasonic motors are known. For example, an example of such Ultrasonic motors is disclosed also in Japanese Patent Laid-Open No. IIE 1-283072/1989. FIG. 14 of the attached drawings is a schematic view showing a principal portion of the conventional ultrasonic motor. The ultrasonic motor is an ultrasonic oscillation-wave motor for friction-driving a movable body 113 which is in contact with an oscillation body 112 through an oscillation surface, by a successive or progressive oscillation wave which is generated on the oscillation body 112 which is joined to a piezoelectric element 11, in FIG. 14. The ultrasonic motor is formed by a cemented earbide material in which hard alumite treatment (the registered name, in Japan, of a method in which aluminum is anodic-oxidized to form a corrosion resistant oxide film) due to an anodic oxidation method is applied to any one of a friction surface of the oscillation body 112 and a friction surface of the moving body 113, and the other friction surface is formed by a cemented carbide material which consists of a nickel-phosphorus group alloy containing one or more of boron carbide, boron titanium and boron nitride.
It is aimed that service life of the ultrasonic motor is improved by a sliding element due to the hard alumite, and a driving force is improved by driving of the moving body due to a high .mu. friction surface (a friction surface high in coefficient of friction).
By the way, such combination of the conventional sliding elements is an extremely effective means. However, there are still many problems if a point of service life is considered. That is, the service life of the above-described conventional ultrasonic motor is still short as compared with service life of an electromagnetic motor. Practical points obstruct or hinder the diffusion or the spread of the ultrasonic motor. The problems of the service life will hereunder be described.
In a case where abrasion is generated, hard alumite on the side of the moving body is shaved so that flour in the form of powder (dimension or size thereof is of the order of sub-.mu.m) and flour in the form of flake (dimension or size thereof is of the order of several tens of .mu.m) are generated. Generation of the flour in the form of flake results from falling-off or coming-off phenomena in the vicinity of a surface of the hard alumite. This results from the fact that crystal structure of the hard alumite is weak.
Once the falling-off phenomena occurs, the flour in the form of flake gets into a location between the moving body and the oscillating body and performs an action much like an abrasion grain so that the falling-off phenomena is promoted or strengthened. That is, the flour in the form of flake shaves the surface of the hard alumite while rolling a location between frictional surfaces. At this time, plenty of or a large quantity of minute or fine flour in the form of powder is generated from the surface of the hard alumite so that the surface of the hard alumite is further shaved. Accordingly, the service life of the hard alumite, that is, the service life as the ultrasonic motor is noticeably or remarkably reduced.
FIG. 11 is a perspective view showing, in enlargement, a cross-section of the above-described conventional hard alumite.
Alumite 1 is a corrosion resistant oxide film which is formed by anodizing of aluminum 3. In this connection, a barrier layer 2 is an intermediate element between the alumite 1 and the aluminum 3, and is expressed by Al.sub.2 +Al.sub.2 O.sub.3.H.sub.2 O.
Immediately after electrolysis, the alumite 1 is brought to a porous oxide film .gamma.-Al.sub.2 O.sub.3 in which a plurality of minute bores or small holes are formed in a surface of the alumite 1. Under this condition, however, the alumite 1 is lacking in durability. Accordingly, sealing is normally performed due to nickel acetate or the like so that the small holes 4 are closed up or filled up.
As shown in FIG. 11, however, sealing is performed only up to a range 105 of several .mu.m from the surface of the alumite 1 by the sealing due to the above-described nickel acetate or the like. That is, sections of the respective small holes 4 from lower portions to bottom portions thereof are brought to a hollow condition. Further, this phenomena is remarkably seen as film thickness of the alumite 1 is thick. If a part of the surface of the alumite 1 falls off by abrasion, a plurality of hollow small holes 4 appear in the surface of the alumite 1. This weakens or reduces the strength of the alumite 1 per se. The falling-off phenomena becomes more and more violent so that abrasion is promoted.
On the other hand, FIG. 12 is a perspective view showing, in enlargement, an example of each of corners of the above-described alumite 1. As shown in FIG. 12, however, the alumite 1 is not formed on a corner 107. This is due to the fact that the alumite 1 has such a property as to be grown on the surface of the aluminum 3 only in a vertical direction. Thus, the alumite 1 is brought to such a condition that the alumite 1 is broken at the corner 107 and a cross-sectional surface thereof is exposed. Under this condition, if a force is applied to the corner 107 from tile outside, such a phenomena occurs that a small piece 108 is missing or is omitted from the corner 107, and the alumite 1 is broken or collapsed from the falling-off portion.
FIG. 13 is an enlarged perspective view showing another example of the corners of the above-described alumite 1 and is an example in which, as shown in FIG. 13, chamfering in the form of C-plane applied to the corner. Also in this case, however, the alumite 1 is brought to a broken condition, and a plurality of small pieces 108 are left out or are missing from the alumite 1 similar to the case illustrated in FIG. 12. The small pieces 108 are larger than the aforementioned flour in the form of flake and further promote an action of the abrasion grain.